1. Viruses
By Mr. “Are you a Zombie” Chapman

2. Is a Virus a Living Organism?
• Properties of life
• Cellular Respiration
• Reproduction
• Metabolism
• Homeostasis
• Heredity
• Growth and development

3. Viruses are not living organisms
Viruses do not
- Reproduce (replicate inside HOST)
– Grow
– Maintain homeostasis
– Metabolize
Viruses do
– Infect cells and use the host cell to make
more viruses
– Cause disease in many organisms

4. Parts of a Virion (a virus particle)
Nucleic Acid – RNA or • Capsid – protein coat that
DNA surrounds the DNA or
RNA in a virus

5. Parts of a Virion
Lipid Envelope– a lipid membrane around the capsid.
Membrane is created by using the host cell membranes.
Helps the virus enter new cells in the host. Membranes’
recognize each other.

6. What is DNA
• DNA is found where in the cell?
• Nucleus
• DNA contains all genes and
characteristics for an organism.
• What are the four nucleotides that make
up DNA?
• DNA made up of A, T, C, G
• Double strand

7. What is RNA
• RNA carries info from DNA in nucleus to
ribosomes where proteins (characteristics)
are assembled.
• RNA is made up of 4 nucleotides:
• A, U, G, C and single strand
• RNA is used to make what?
• RNA makes protein

8. RNA or DNA?
Viruses with RNA
– Human immunodeficiency virus (HIV)
– Influenza viruses (Flu)
– Rabies
Viruses with DNA
– Warts
– Chickenpox
– Herpes
– Smallpox

9. Virus Shapes
Helical
Rodlike with capsid proteins winding around the
core in a spiral
Examples: Rabies, Measles

10. Measles
• • Mild fever of 102 °F or lower
• Headache
• Stuffy or runny nose
• Red, inflamed eyes
• Enlarged, tender lymph nodes at the base of the skull, the back of the
neck, and/or behind the ears
• Fine, pink rashes that begins on the face and quickly spreads to the trunk,
the arms, and then the legs before disappearing in the same sequence
• Aching joints, especially in young women
Causes
Rubella is caused by a virus that is enveloped and has a single-stranded
RNA genome. It is a contagious disease and can spread with the cough or
sneeze of an infected person. It can alternately spread by direct contact with
an infected person's respiratory secretions, including mucus. It can also
travel from a pregnant woman to her unborn child (congenital rubella
syndrome [CSR]). A person infected with rubella is contagious from one
week before the start of the rash until about one to two weeks after the rash
disappears

11. Herpes
• Herpes simplex type 1: this type of Herpes virus causes the aggravating lip and mouth blisters
and sores called 'cold sores' or fever blisters, and technicall called Herpes labialis. It is HIGHLY
infectious and can easily be spread by physical contact with an infected persons saliva
• Herpes simplex Type 2: is the version of the virus that is responsible for genital herpes, the
dreaded Sexually Transmitted Infection (STI) or Sexually Transmitted Disease (STD) - referred to
as Herpes genitalis
• Herpes zoster: Is the other major type of Herpes virus which affects many children in the form of
Chicken Pox which also appears as a blister-like rash all over the body. You can also get
Chicken Pox as an adult, but the illness can be more severe and unpleasant, so in many ways it
is a good thing to get it out-of-the-way as a child. Although you will not get Chicken Pox again
once your natural immunity has developed you will still have this Herpes virus in your system.
• In later life if you become run down or highly stressed you may experience another form of
outbreak of painful blisters that develop along certain nerve meridians around te torso, for
instance, or in the scalp - this other 'herpetic' illness that is called Shingles.

12. Virus Shapes
Polyhedral
Has many sides
Most polyhedral capsids have 20 triangular
faces.
Ex. Herpes, Chickenpox, Polio

13. Polio
• Poliovirus only circulates in humans. It is spread by the faecal–oral and oral-oral (respiratory) routes.
• Infected people are most contagious shortly before and after onset of clinical illness when the virus is present in
the throat and excreted in high concentration in the faeces.
• Recipients of OPV (oral polio vaccine) can also pass on poliovirus to non-immune people as the virus persists in
the throat for 1 – 2 weeks and is excreted in the faeces for several weeks.
• Incubation period commonly 6–20 days with a range of 3–35 days.
• Up to 95% of all polio infections are asymptomatic. Infected persons without symptoms shed virus in the stool.
• Approximately 4%–8% of polio infections consist of a minor, nonspecific illness. Three syndromes observed with
this form of poliovirus infection are upper respiratory tract infection (sore throat and fever), gastrointestinal
disturbances (nausea, vomiting, abdominal pain, constipation or, rarely, diarrhoea), and influenza-like illness.
These syndromes are indistinguishable from other viral illnesses.
• symptoms of stiffness of the neck, back, and/or legs
• Less than 1% of all polio infections result in flaccid paralysis. The frequency of paralytic disease increases with
age. Paralytic symptoms generally begin 1 to 10 days after prodromal symptoms and progress for 2 to 3 days.
• Generally, no further paralysis occurs after the temperature returns to normal.

14. Virus Shapes
Bacteriophages - Polyhedral capsid
attached to a helical tail. Viruses that
attack bacteria. (Ex. E. coli)

15. How do viruses
replicate?
2 methods of
replication:
1. Lytic Cycle – the
virus enters the cell,
replicates itself
hundreds of times,
and then bursts out of
the cell, destroying it.

16. In the lytic cycle, the
virus reproduces
itself using the host
cells' machinery.
The red spiral lines
in the drawing
indicate the virus's
genetic material.
The orange portion
is the outer shell
that protects it.

17. Virus Replication
2. Lysogenic Cycle –
the virus DNA
integrates with the
host DNA and the
host’s cell helps
create more virus
DNA. An
environmental change
may cause the virus
to enter the Lytic
Cycle.

18. In the lysogenic
cycle, the virus
reproduces by
first injecting its
genetic material,
indicated by the
red line, into the
host cell's genetic
instructions.

19. Virus Reproduction
• When a virus inserts its genetic material
into a host’s DNA, it is called a provirus.
• If virus has RNA and enters a host’s cells,
it can sometimes turn its RNA into DNA.
• Reverse Transcriptase – turns RNA into
DNA (called retrovirus; ex. HIV); DNA
instructs cell to make more viruses

20. Viruses Enter Living Cells
Viruses enter cells by punching a hole in the
cells wall and injecting its DNA

21. Viruses Enter Living Cells
Viruses enter plant cells through tiny rips in
the cell wall.
Viruses enter animal cells by endocytosis.

22. Mutating viruses
Viruses can mutate when they copy the
genetic material
– Copy something wrong
– Mistake proves useful
– More powerful virus (more infectious)
Viruses that mutate
Influenza
Viruses don’t mutate often:
HIV

23. Viruses are host cell specific.
Most viruses are restricted to certain kinds
of cells (those that infect plants cannot
infect animal cells).
Some viruses are also specific to certain
species of animals.
Why?
Scientists think that viruses originated from
escaped genetic material from host cells.

24. Hunt for new viruses
• http://www.ted.com/talks/nathan_wolfe_hunts_

26. The spread of West Nile virus (1999 –
2002) – bird, horse, mosquito or human

27. Viruses can be beneficial…
Bacteriophages – attack & destroy bacteria
http://dvc.infohio.org/index.php?option=com_content&view=article&id=11&Itemid=14&
Baculovirus – ebola-like virus that attacks
insects
– Could use for pest control in crops
• Cabbage loopers eat
cabbage crops
• Virus can kill pests in days

28. Also important…
Any agent (not just viruses) that causes
disease is a pathogen.
Some viruses replicate very slowly and only
cause damage when the conditions are
“right”. (cold sores)

29. Vaccinations/Immunization
• http://video.about.com/pediatrics/Immunization
• http://video.about.com/pediatrics/Vaccination.h

30. Human Immunodeficiency Virus
(HIV)
Acquired Immune Deficiency
Syndrome (AIDS)

31. Basic Structure
• Viral envelope – lipid bilayer; glycoproteins
protrude from surface
– Glycoproteins enable virus to recognize
surface proteins of special immune cells and
to enter the cell (like a key to the cell’s door)
• 2 strands RNA – only 9 genes; 3 are
found in many viruses (structural proteins)
• Reverse Transcriptase – turns RNA into
DNA (this makes HIV a retrovirus); DNA
instructs cell to make more viruses

33. HIV Making Factories
• Virus enters cell through endocytosis
• Virus replicates RNA to DNA with reverse
transcriptase

34. How Is HIV Spread?
• Sexual contact
• Sharing contaminated needles
• Blood transfusions
• Breast feeding (mother to baby)
• Mother to baby during pregnancy or birth

35. • DNA enters nucleus & binds with host DNA
•mRNA is created
(carries
instructions for
making new viral
proteins) and
leaves nucleus
•Uses host cell’s
enzymes to make
new viruses
• New virions exit cell through exocytosis to infect
other cells (notice cell isn’t destroyed)

36. Think about it…
• In the US, there is better than a 1/1000 chance of
contracting HIV during unprotected sex
• A person can be contagious for more than 10 years before
any sign of the disease is apparent
• HIV becomes AIDS when the number of immune cells drops
below a predetermined number
• No one dies from HIV or AIDS; people die from secondary
infections (ranging from the common cold to cancer)
• More than 3 million people (size of Chicago) die each year
• There are approx. 14,000 new cases of HIV
worldwide every day